ERYLUS SOLLASII. 275 



massive, flattened, or drawn out so as to appear like strings of beads. Some of 

 the granules forming these groups are similar to the granules in the granular 

 cells, others are larger. They seem to be remnants of disintegrated granular cells. 



Canal-system. The afferent apertures, which, as mentioned above, generally 

 form groups on the surface, are uniporal. They are always circular but they 

 differ very considerably in size, thgir diameter varying between 70 and 520 /t. 

 The largest pores were observed in race I, form C, and in race III. From each 

 pore a canal leads vertically downwards. Tliis canal penetrates the cortex and 

 opens out into one of the subcortical cavities which underlie the poral areas of 

 the cortex. Its proximal opening into the subcortical cavity is surrounded by a 

 chonal sphincter usually more or less contracted, but only rarely completely 

 closed. The canals leading down from small jwres are distended, those leading 

 down from large pores constricted below the entrance. I am inclined to ascribe 

 these differences and also, to a great extent, the differences in the width of the 

 pores themselves, to tlifferences in the degree of contraction. The afferent canals, 

 which arise from the subcortical cavities and lead down into the choanosome, 

 are not particularly wide and divide into numerous narrow branch-canals which 

 supply the flagellate chambers. The latter (Plate 1, fig. 4) are spherical or 

 somewiiat compressed in the direction of their axis, and measure about 20 /< 

 in diameter. The efferent canals join to form lacunose cavities, which some- 

 times attain a very considerable width (Plate 1, fig. 1). They open out on the 

 surface with the oscules described above. 



Skeleton. Loose strands of rhabcl megascleres traverse the choanosome. 

 Their distal portions extend more or less radially and tliey terminate just below 

 the coi'tex. Triaenes with radial, centripetally directed rhabdomes are quite 

 abundant in the subcortical layer. In some of the sections a few spicules of 

 this kind have also been found in the interior of the choanosome. I do not 

 consider that as their natural position, however, and believe that these triaenes 

 were brought there from the subcortical layer in cutting the section. No mega- 

 scleres protrude bej'ond the surface, and this is entirely destitute of a spicule- 

 fur. Microrhabds occupy in large numbers the outer layer of the cortex and are 

 found in smaller nunibers also in the choanosome, chiefly in its distal parts. In 

 the outer, cortical layer of the cortex these niicrorhabds are not regularly ar- 

 ranged; some are situated paratangentially, others obliquely, and others radially. 

 The middle layer of the cortex is occupied by dense masses of aspidasters, 

 most of which are arranged paratangentially, with their broad faces parallel 

 to the outer surface. Only around the pores some of them are differently sit- 



